In 1971 Knudson proposed that tumorigenesis requires two genetic events or "hits" based on statistical analyses of malignancies in cancer predisposition syndromes. Mapping and later cloning of the retinoblastoma (Rb) gene provided direct experimental support for the "two hit" theory. Multiple endocrine neoplasia type 1 (MEN1), characterized by parathyroid hyperplasia and neoplasms of the pituitary and pancreatic islet cells, resembles hereditary Rb in the number, distribution, and relatively early age of onset of neoplasms. Larsson et al. recently mapped the MEN1 gene to chromosome 11q by linkage studies and showed loss of heterozygosity for chromosome 11 RFLPs in two tumors from MEN1 patients. It seems likely that neoplasia in this disorder arises through a two hit mechanism. The aim of the proposed project is to refine the map location of MEN1, chromosome walk to the locus, determine if it codes for an expressed gene, and study its relation to other cancer predisposition genes. Mapping will proceed by linkage studies in several kindreds and by comparing the areas of loss of heterozygosity for RFLPs in a series of tumors with partial deletions to define the smallest region of overlap. Pulsed field gel electrophoresis (PFGE) will be used to detect a fragment containing the two closest flanking RFLPs. Depending on the distance between these markers, either the entire region will be cloned in S. cerevisiae or a series of subclones from the region will be ordered using PFGE of partial DNA digests. In a manner similar to that used to isolate the Rb gene, probes that are deleted in all tumors will be isolated from this region. If the MEN1 gene functions in a manner analogous to the Rb gene, some probes will detect and RNA transcript in normal tissue and fail to detect a transcript in tissue from MEN1-related tumors. Cloned cDNA from such a transcript will be used to determine the pattern of expression in various tissue types, and the sequence will be compared with that of the Rb gene and others.